Role of MeCP2 in Shaping the Histopathological Heterogeneity of Ampullary Carcinoma.

Ampullary carcinoma exhibits marked histological heterogeneity. Although genetic alterations partially account for this diversity, the contribution of epigenetic regulation remains largely unexplored. To elucidate the epigenetic alterations underlying this phenotypic heterogeneity, we investigated methyl-CpG-binding protein 2 (MeCP2) and its downstream target CDX2, and versican (VCAN), a major extracellular matrix proteoglycan implicated in tissue remodeling and tumor-stroma interactions. Seventeen surgically resected cases were analyzed using an integrative approach combining immunohistochemistry, spatial transcriptomics, methylation mapping, electrophoretic mobility shift assays (EMSA), and bioinformatic profiling. In non-neoplastic mucosa, MeCP2 and CDX2 showed reciprocal nuclear expression, a relationship partially preserved in differentiated adenocarcinomas. Spatial transcriptomics identified VCAN as a key MeCP2-associated target gene. Unexpectedly, VCAN, although detectable in MeCP2-negative carcinoma cells, was abundantly expressed in MeCP2-positive cancer-associated fibroblasts (CAFs). Notably, such transcriptional activation by MeCP2, rather than repression, has been reported in neural tissue by previous studies, indicating a conserved mechanism of context-dependent gene regulation. EMSA further demonstrated that hydroxymethylated CpG sites within the VCAN promoter specifically recruited MeCP2, which interacted with CREB to activate VCAN transcription. These findings reveal a dual role of MeCP2: its loss contributes to epithelial heterogeneity, whereas its retained function in CAFs promotes stromal remodeling through VCAN activation.